In a net game, the Thing_Remove() ACS function will not update the scoreboard monster counter on the client; and neither will changing the friendliness of a monster using SetActorProperty() and APROP_Friendly.

These all do affect, for example, the LEVELINFO_TOTAL_MONSTERS value obtainable with GetLevelInfo() in ACS, and the scoreboard counter will also be corrected after reconnecting (this is known to be true at least for the Thing_Remove case).